Crystal diodes for a p-type semiconductor and the formation of n-type semiconductor p-n junction, in the space-charge layer is formed on both sides of the interface, and has since built an electric field. When there is no external voltage, the result of p-n junction on both sides of carrier concentration gradient diffusion current and built an electric field of drift current in electrical equilibrium is the same.
When the outside when there is a positive voltage offset, external electric field and build mutual inhibition effect of the electric field to increase the diffusion of carriers has caused the forward current.
When the outside when there is a reverse-bias voltage, construction of electric field by external electric field and further strengthen and formed a certain reverse voltage range of the reverse bias voltage value of the reverse saturation current I0.
When reverse voltage to a certain degree, the electric field strength of the p-n junction in the space-charge layer carrier multiplication process reaches a critical value, produces a large number of electron-hole pairs, is so large the reverse breakdown current is produced, known as the diode breakdown phenomenon.